Barrier coatings

ABSTRACT

A barrier coating of organic-inorganic composition, the barrier coating having optical properties that are substantially uniform along an axis of light transmission, said axis oriented substantially perpendicular to the surface of the coating.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

This invention was made with Government support under contract numberRFP01-63GE awarded by United States Display Consortium and Army ResearchLaboratory. The Government has certain rights in the invention.

BACKGROUND

The invention relates generally to barrier coatings. More specifically,the invention relates to barrier coatings that are used inoptoelectronic devices.

Optical and optoelectronic devices that are susceptible to reactivechemical species normally encountered in the environment, requirebarrier coatings with desirable light transmission properties.

Multilayer barrier coatings desirably are effective barriers againstreactive species like oxygen and water vapor. To achieve desired barrierproperties it is known in the art to try find layers of materials ofvarious organic and inorganic compositions. Such materials commonly havedifferent indices of refraction, normally resulting in degradation inoptical transmission through the barrier layer. Prior approaches havefocused on engineering the thickness of the layers to take advantage ofmultiple-interference to improve light transmission efficiency. However,one has to retain certain thickness of the layers in order to maintainthe performance of the barrier, and thus it is not always easy toengineer the thickness. Furthermore, in a mass production environment itis difficult to achieve exact thickness control of the layers. Also, ithas been suggested that in multilayer barriers, the interface betweenlayers of different materials is generally weak due to incompatibilityof adjacent materials and the layers, thus, are prone to be delaminated.

Organic-inorganic coating compositions desirably may be used to minimizemoisture and oxygen permeation rates through the barrier coating. It hasbeen speculated that the organic zone sandwiched between two inorganiczones decouples the defects in one inorganic zone to another. Thickorganic zones in the coating are effective in decoupling the defects.However, inorganic materials typically have a refractive index n about1.8 and organic materials typically have a refractive index n about 1.5.Due to the refractive index mismatch, large amplitude interferencefringes are observed with thick organic zones in the coating. Desiredoptical performance achieved by maintaining organic zone thickness asthin as possible, degrades the barrier properties of the coating.

Therefore, there is need for barrier coatings that are not only robust,having low diffusion rates for environmentally reactive species, butalso have desirable optical properties and can easily be mass produced.

BRIEF DESCRIPTION

The present invention addresses the needs discussed above. One aspect ofthis invention is a composite article comprising a barrier coating oforganic-inorganic composition, the barrier coating having opticalproperties that are substantially uniform along an axis of lighttransmission, said axis oriented substantially perpendicular to thesurface of the coating.

Another aspect of the invention is a method for depositing anorganic-inorganic barrier coating. The method comprising the steps ofproviding at least one surface for deposition; depositing reaction orrecombination products of reacting species on the surface; changing thecompositions of the reactants fed into the reactor chamber during thedeposition to form a compositionally organic-inorganic coating, with atleast one substantially organic zone and at least one substantiallyinorganic zone; and performing refractive index modification of at leastone inorganic zone by varying the precursor gas composition, saidrefractive index of the inorganic zone being adjusted to provide asubstantially uniform refractive index along an axis of lighttransmission through said barrier coating.

A further aspect of the invention is a device assembly comprising adevice, at least one surface of which is coated with at least onebarrier coating of organic-inorganic composition, the composition ofwhich varies across the thickness of the coating and has substantiallyuniform refractive index along the axis of light transmission, the axisoriented substantially perpendicular to the surface of the coating.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 graphically shows light transmittance through identicalsubstrates having barrier coatings with and without refractive indexmatching.

FIG. 2 shows schematically an embodiment of a barrier coating of thepresent invention.

FIG. 3 shows light transmittance spectra for barrier coatings of thepresent invention with varying number of zones and varying zonethicknesses.

FIG. 4 shows schematically a first embodiment of a composite articlewith a barrier coating.

FIG. 5 shows schematically a second embodiment of a composite articlewith a barrier coating.

FIG. 6 shows schematically a third embodiment of a composite articlewith a barrier coating.

FIG. 7 shows variation in refractive index and extinction coefficientwith variation in oxygen mole fraction in precursor feed gas duringdeposition.

FIG. 8 shows calculated visible light transmittance spectra as afunction of oxygen mole fraction in feed gas during deposition.

DETAILED DESCRIPTION

Light emitting and light absorbing materials and electrode materials inoptoelectronic devices, especially in organic optoelectronic devices,are all susceptible to attack by reactive species existing in theenvironment, such as oxygen, water vapor, hydrogen sulfide, SO_(x),NO_(x), solvents, etc. Barrier coatings engineered to affect lighttransmission only to a small extent are useful in extending the devicelifetime without degrading the overall device efficiency, thus renderingthem commercially viable. Desirable barrier properties are achieved inthe coating of the present invention by using an organic-inorganiccomposition and desirable light transmission is achieved by matchingrefractive indices of inorganic zones and organic zones in the coating.

One aspect of this invention is a composite article comprising a barriercoating of organic-inorganic composition, the barrier coating havingoptical properties that are substantially uniform along an axis of lighttransmission oriented substantially perpendicular to the surface of thecoating. “Substantially perpendicular” means within 15 degrees eitherside of a perpendicular to a tangent drawn at any point on the surface.In a preferred embodiment, the substantially uniform optical propertiesprovides for a coating with a substantially uniform refractive index.“Substantially uniform refractive index” means the refractive index ofany zone in the coating is within 10% of any other zone in the coatingfor a selected wavelength. The barrier coating preserves colorneutrality by exhibiting substantially uniform light transmission.“Substantially uniform light transmission” means at any selectedwavelength in a selected wavelength range, the transmission is within10% of the average light transmission for the wavelength range, in otherwords, the barrier coating does not substantially differentiallyattenuate wavelengths within the selected wavelength range. The barriercoating is constructed with zones of various compositions. The oxygenand water vapor barrier properties are enhanced by the inorganic-organiccomposition. Optical loss due to interference resulting from differingrefractive indices of the zones of various compositions is overcome bydepositing substantially uniform refractive-index materials. The desiredtransmissivity is achieved by matching the refractive indices of zonesin the coating.

In optoelectronic devices one of the important performance parameters isoptical efficiency. Therefore it is desirable that any coating used insuch a device to enhance other performance parameters, does notcompromise the optical efficiency due to light absorption or otherfactors. Therefore it is important that barrier coatings besubstantially transparent. The term “substantially transparent” meansallowing a total transmission of at least about 50 percent, preferablyat least about 80 percent, and more preferably at least 90 percent, oflight in a selected wavelength range. The selected wavelength range canbe in the visible region, the infrared region and the ultravioletregion. For example, a 5 mil polycarbonate substrate with a barriercoating of the present invention, light transmittance along the axis oflight transmission is greater than 85% for all wavelengths in thevisible light wavelength region about 400 nanometers to about 700nanometers. FIG. 1 compares the visible light transmittance through asubstrate with a barrier coating of organic-inorganic compositionwithout refractive index matching (a) with a refractive index matchedbarrier coating of organic-inorganic composition (b). FIG. 1 shows atransmittance greater than 85% for the visible wavelength with no largeamplitude interference fringes for the barrier coating of the presentinvention. Therefore the barrier coating of the present invention isdesirably substantially transparent in the visible wavelength range.

The barrier coating of the present invention consists of at least onesubstantially transparent inorganic zone and at least one substantiallytransparent organic zone having low permeability of oxygen or otherreactive materials present in the environment. By low permeability it ismeant that the oxygen permeability is less than about 0.1 cm³/(m² day),as measured at 25° C. and with a gas containing 21 volume-percent oxygenand the water vapor transmission is less than about 1 g/(m² day), asmeasured at 25° C. and with a gas having 100-percent relative humidity.

Referring to drawings in general and to FIG. 2 in particular, theillustrations are for the purpose of describing an embodiment or aspectof the invention and are not intended to limit the invention. FIG. 2shows schematically a substantially organic zone 12, a substantiallyinorganic zone 14 and an organic-inorganic interface zone 16 The term“substantially organic” means the composition is over 90% organic. Theterm “substantially inorganic” means the composition is over 90%inorganic. Although, any number of zones can be present in the barriercoating, at least two, a substantially organic zone 12 and asubstantially inorganic zone 14, is suitable for reduction of moisture,oxygen and other reactive species. Typical thickness of respectivesubstantially organic zones 12 is 100 nanometers to 1 micron. Typicalthickness of respective substantially inorganic zones 14 is 10nanometers to 100 nanometers. Typical thickness of respectivetransitional zones 16 is 5 nanometers to 30 nanometers. In oneembodiment, the substantially organic zone 12 is of uniform composition.In another embodiment, the substantially organic zone 12 is of acomposition that varies across the thickness of the zone. In anotherembodiment all substantially organic zones 12 in a barrier coating areof same composition. In another embodiment at least two of the organiczones 12 are of different composition. In one embodiment, thesubstantially inorganic zone 14 is of uniform composition. In anotherembodiment, the substantially organic zone 14 is of a composition thatvaries across the thickness of the zone. In another embodiment, allsubstantially organic zones 14 in a barrier coating are of samecomposition. In another embodiment at least two of the organic zones 14are of different composition. Other embodiments may include transitionalzones 16 that are neither substantially organic nor substantiallyinorganic. It should be clearly understood that the zones are notlayers. The zones do not have distinct boundaries.

Thus, a coating of the present invention does not have distinctinterfaces at which the composition of the coating changes abruptly. Itshould also be noted that the composition of the barrier coating doesnot necessarily vary monotonically from one surface to the other surfacethereof. A monotonically varying composition is only one case of barriercoating of the present invention.

FIG. 3 shows transmission spectra for barrier coatings with varyingnumber of zones and varying organic zone thickness. Transmission spectraas shown in FIG. 3 for barrier coatings with 100 nm silicon oxycarbidesubstantially organic zone between two 30 nm silicon oxynitridesubstantially inorganic zones (a), with 300 nm silicon oxycarbidesubstantially organic zone between two 30 nm silicon oxynitridesubstantially inorganic zones (b), with 600 nm silicon oxycarbidesubstantially organic zone between two 30 nm silicon oxynitridesubstantially inorganic zones (c) and with two 300 nm silicon oxycarbidesubstantially organic zone alternating with three 30 nm siliconoxynitride substantially inorganic zones, clearly demonstrate that thetransmission efficiency of the barrier coating is affected only in asmall way by increasing the number of zones or by increasing thicknessof the organic zones in the coating. This invention thereby preservesgood transmission efficiency even with thick organic zones and withmultiple organic and inorganic zones, which will aid in improving thebarrier properties of the coating. All barrier coatings in this examplehave 10 nm transitional zones between the substantially organic andsubstantially inorganic zones.

Suitable coating compositions of regions across the thickness areorganic, and inorganic materials and combinations thereof. Thesematerials are typically reaction or recombination products of reactingplasma species and are deposited onto the substrate surface. Organiccoating materials typically comprise carbon, hydrogen, oxygen, andoptionally other minor elements, such as sulfur, nitrogen, silicon,etc., depending on the types of reactants. Suitable reactants thatresult in organic compositions in the coating are straight or branchedalkanes, alkenes, alkynes, alcohols, aldehydes, ethers, alkylene oxides,aromatics, etc., having up to 15 carbon atoms. Inorganic coatingmaterials typically comprise oxide; nitride; carbide; boride; orcombinations thereof of elements of Groups IIA, IIIA, IVA, VA, VIA,VIIA, IB, and IIB; metals of Groups IIIB, IVB, and VB; and rare-earthmetals.

In one embodiment of the composite article of the present invention, asshown in FIG. 4, at least one barrier coating 10 is disposed on at leastone surface of an element or substrate 20, of the composite article 30.In another embodiment of the composite article of the present invention,as shown in FIG. 5 at least one barrier coating 10 disposed on at leastone surface of more than one element 20 of the composite article. In athird embodiment of the composite article 30 of the present invention,as shown in FIG. 6, at least one barrier coating 10 encapsulates atleast one substrate or element 20 of the composite article 30.

In another embodiment of the composite article, at least one element isan optoelectronic element. In a further preferred embodiment of thecomposite article, the optoelectronic element is an organic element. Inone embodiment of the composite article the optoelectronic element is anelectroluminescent element. In another embodiment of the compositearticle the optoelectronic element is a photoresponsive element.

In another embodiment, the composite article includes a polymericsubstrate and an active element, which is an organic electroluminescentelement.

The composite article may include additional elements such as, but notlimited to, an adhesion layer, abrasion resistant layer, chemicallyresistant layer, photoluminescent layer radiation-absorbing layer,radiation reflective layer, conductive layer, electrode layer, electrontransport layer, hole transport layer and charge blocking layer.

Another aspect of the invention is a method for depositing the barriercoatings of organic-inorganic composition. The method comprising thesteps of providing at least one surface for deposition, depositingreaction or recombination products of reacting species on the surface,changing the compositions of the reactants fed into the reactor chamberduring the deposition to form an organic-inorganic coating with at leastone substantially organic zone and at least one substantially inorganiczone, and performing refractive index modification of at least oneinorganic zone by varying the precursor gas composition, the refractiveindex of the inorganic zone being adjusted to provide a substantiallyuniform refractive index along an axis of light transmission through thebarrier coating

A bulk material or a substrate having a surface for deposition typicallyis a single piece or a structure comprising a plurality of adjacentpieces of different materials. Non-limiting examples of a substrateinclude a rigid transparent glass and a flexible or rigid polymericsubstrate.

The coating can be formed using one of many deposition techniques, suchas plasma-enhanced chemical-vapor deposition, radio-frequencyplasma-enhanced chemical-vapor deposition, microwave plasma enhancedchemical vapor deposition, expanding thermal-plasma chemical-vapordeposition, sputtering, reactive sputtering,electron-cyclotron-resonance plasma-enhanced chemical-vapor deposition,inductively-coupled plasma-enhanced chemical-vapor deposition, andcombinations thereof. Information regarding all deposition techniques isgenerally known and readily available.

For example, silicon carbide can be deposited on a surface byrecombination of plasmas generated from silane (SiH₄) and an organicmaterial, such as methane or xylene. Silicon oxycarbide can be depositedfrom plasmas generated from silane, methane, and oxygen or silane andpropylene oxide. Silicon oxycarbide also can be deposited from plasmasgenerated from organosilicone precursors, such as Vinyl trimethylsilane(VTMS), tetraethoxysilane (TEOS), hexamethyldisiloxane (HMDSO),hexamethyldisilazane (HMDSN), or octamethylcyclotetrasiloxane (D4).Aluminum oxycarbonitride can be deposited from a plasma generated from amixture of aluminum tartrate and ammonia. Other combinations ofreactants may be chosen to obtain a desired coating composition. Thechoice of particular reactants is within the skills of the artisans. Amixed composition of the coating is obtained by changing thecompositions of the reactants fed into the reactor chamber during thedeposition of reaction products to form the coating.

For example, when the coating on a surface is desired to comprisesilicon nitride, the first reactant gas can be ammonia, and the secondreactant gas can be silane. The relative supply rates of reactant gasesare varied during deposition to vary the composition of the depositedmaterial as the coating is built up. If oxygen is used as an additionalprecursor gas, and the mole fraction of oxygen in the feed gas isincreased from zero, the material deposited on the surface changes fromsilicon nitride to silicon oxynitride. As the oxygen mole fraction inthe reactant gas increases, oxygen starts to replace nitrogen in thedeposited material. Compositional and structural changes occur withincrease in oxygen mole fraction, resulting in refractive indexmodification as well. Therefore, in this example, refractive indexmodification is achieved by varying the mole fraction of a constituentreactant in the precursor. FIG. 7 shows the variation of refractiveindex with variation in oxygen mole fraction, for a precursorcomposition including, ammonia and oxygen. For example, if thesubstantially organic zone of silicon oxycarbide having a refractiveindex at 550 nm of about 1.5 is used in the coating, then asubstantially inorganic zone of silicon oxynitride, at an oxygen molefraction of about 0.25, is also deposited such that the refractive indexof the inorganic zone matches the refractive index of the substantiallyorganic zone of silicon oxycarbide, resulting in a barrier coating oforganic-inorganic composition with substantially uniform refractiveindex.

FIG. 7 shows measured optical properties, refractive index (a) andextinction coefficient (b), of inorganic layers deposited with varyingoxygen mole fraction, obtained by spectroscopic ellipsometry. In thisexample, depending on the oxygen mole fraction in the precursor feedgases, refractive index of the depositing inorganic material varies from1.8 to 1.4. Thus, by selecting a process condition, which results inrefractive index of depositing inorganic material close to that oforganic material, the interference amplitude can be reducedsignificantly. FIG. 7 also indicates that the extinction coefficient (b)does not change enough to significantly affect the absorption of lightthrough the inorganic layers for thicknesses of inorganic layers used inthis invention.

FIG. 8 shows visible light transmittance spectra through the barriercoating for different oxygen mole fractions 0.0 (a), 0.25 (b), 0.5 (c),0.75, (d) and 1.0 (e) in precursor feed gas calculated using measuredoptical properties such as refractive index n and extinction coefficientk. In this example visible light transmittance with minimum interferencefringes are achieved at about 0.25 oxygen mole fraction indicating thatthe refractive index of the inorganic material deposited under thisprocess condition matches the refractive index of the organic materialdeposited

In another embodiment of the present invention, a region between thesubstrate or element with the coating and the coating is diffuse, suchthat there is a gradual change from the composition of the bulk of thesubstrate or element to the composition of the portion of the coating.Such a transition prevents an abrupt change in the composition andmitigates any chance for delamination of the coating. The gradual changeof the coating composition is achieved by the gradual change of theprecursor composition.

A further aspect of the invention is a device assembly comprising adevice, at least one surface of which is coated with at least onebarrier coating, the composition of which varies across the thickness ofthe coating and has substantially uniform refractive index along theaxis of light transmission. Such device assemblies include, but are notlimited to, liquid crystal displays, light emitting devices,photo-responsive devices, integrated circuits and components of medicaldiagnostic systems.

The device assembly may comprise a device disposed on a flexiblesubstantially transparent substrate, said substrate having a firstsubstrate surface and a second substrate surface, at least one of saidsubstrate surface being coated with the barrier coating of the presentinvention.

The barrier coatings of the present invention have many advantages,including being robust against environmentally reactive species, havingdesirable optical properties and being easily mass-produced. Thefundamental advantage of the method of deposition of the presentinvention is that it enables concurrent control of optical and diffusionproperties of barrier coatings by adjusting the deposition parameters.The barrier coatings of the present invention would be useful as barriercoatings in many optical and optoelectronic devices including organiclight-emitting devices and organic photovoltaic devices.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1-24. (canceled)
 25. A method for depositing a barrier coating,comprising the steps of: providing at least one surface for deposition;depositing reaction or recombination products of reacting species on thesurface; changing the compositions of the reactants fed into the reactorchamber during the deposition to form a compositionallyorganic-inorganic coating; said coating comprising at least onesubstantially organic zone and at least one substantially inorganiczone; performing refractive index modification of the at least oneinorganic zone by varying the precursor gas composition, said refractiveindex of the inorganic zone being adjusted to provide a substantiallyuniform refractive index along an axis of light transmission throughsaid barrier coating.
 26. The method of claim 25, wherein saiddepositing is selected from the group consisting of plasma-enhancedchemical-vapor deposition, radio-frequency plasma-enhancedchemical-vapor deposition, expanding thermal-plasma chemical-vapordeposition, sputtering, reactive sputtering,electron-cyclotron-resonance plasma-enhanced chemical-vapor deposition,inductively-coupled plasma-enhanced chemical-vapor deposition, andcombinations thereof.
 27. The method of claim 25, wherein the barriercoating material is selected from the group consisting of organic,inorganic materials, and combinations thereof.
 28. The method of claim27, wherein the inorganic material are selected from the groupconsisting of oxide, nitride, carbide, boride and combinations there ofelements of Groups IIA, IIIA, IVA, VA, VIA, VIIA, IB and IIB, metals ofGroups IIIB, IVB, and VB and rare-earth metals.
 29. The method of claim27, wherein the organic barrier coating material comprising carbon,hydrogen and oxygen.
 30. The method of claim 29, wherein said organicmaterial further comprising sulfur, nitrogen, silicon and otherelements. 31-86. (canceled)
 87. A method comprising: providing a devicedisposed on a substrate; and coating a surface of said device with abarrier coating of organic-inorganic composition, the barrier coatinghaving optical properties that are substantially uniform along an axisof light transmission, said axis oriented substantially perpendicular tothe surface of the coating, wherein the barrier coating comprises atleast one zone substantially organic in composition and at least onezone substantially inorganic in composition.
 88. The method of claim 87,wherein the refractive index of the barrier coating is substantiallyuniform along the axis of light transmission.
 89. The method of claim87, wherein light transmittance through the barrier coating, along theaxis of light transmission, is greater than 85% for all wavelengths in aselected wavelength range.
 90. The method of claim 89, wherein lighttransmittance through the barrier coating is greater than 85% in theselected wavelength range between about 400 nanometers to about 700nanometers.
 91. The method of claim 87, wherein said optical propertiesof said barrier coating comprise substantially uniform lighttransmittance for all wavelengths within a selected wavelength range.92. The method of claim 91, wherein light transmittance through thebarrier coating is substantially uniform for the selected wavelengthrange between about 400 nanometers to about 700 nanometers.
 93. Themethod of claim 87, wherein a transmission rate of oxygen through thebarrier coating is less than about 0.1 cm.sup.3/(m.sup.2 day), asmeasured at 25.degree. C. and with a gas containing 21 volume-percentoxygen.
 94. The method of claim 87, wherein a transmission rate of watervapor through the barrier coating is less than about 1 g/(m.sup.2 day),as measured at 25.degree. C. and with a gas having 100-percent relativehumidity.
 95. The method of claim 87, wherein the barrier coatingcomprises zones of substantially homogenous composition.
 96. The methodof claim 95, wherein the barrier coating further comprises transitionalzones of mixed organic and inorganic composition.
 97. The method ofclaim 87, wherein the barrier coating material is selected from thegroup consisting of organic, inorganic materials, and combinationsthereof.
 98. The method of claim 97, wherein the inorganic materials areselected from the group consisting of oxide, nitride, carbide, borideand combinations there of elements of Groups IIA, IIIA, IVA, VA, VIA,VIIA, IB and IB, metals of Groups IIIB, IVB, and VB and rare-earthmetals.
 99. The method of claim 97, wherein the organic barrier coatingmaterial comprises carbon, hydrogen and oxygen.
 100. The method of claim99, wherein said organic material further comprises sulfur, nitrogen,silicon and other elements.
 101. The method of claim 87, furthercomprising coating a surface of said substrate with said barriercoating.
 102. The method of claim 87, wherein at least one barriercoating encapsulates the method.
 103. The method of claim 87, furthercomprising encapsulating said device with said barrier coating.
 104. Themethod of claim 87, wherein said device is an optoelectronic element.105. The method of claim 104, wherein the optoelectronic element is anorganic element.
 106. The method of claim 104, wherein theoptoelectronic element is electroluminescent.
 107. The method of claim104, wherein the optoelectronic element is photoresponsive.
 108. Themethod of claim 87, wherein said substrate is substantially transparent.109. The method of claim 87, wherein said substrate comprises a metal.110. The method of claim 87, wherein said substrate comprises glass.111. The method of claim 87, wherein said substrate is flexible.